DOCUMENTED BY BATCHTirzepatide, semaglutide and retatrutide are three synthetic peptides that appear together in the current research literature because they share a common structural lineage in the incretin and glucagon receptor families. This reference compares the three strictly on published chemical identity: registry number, amino-acid chain length, molecular formula and molecular weight, and the receptor-target class assigned to each in the peer-reviewed literature. It makes no statement about use, and all figures below are drawn from PubChem and primary chemical registries.
Why compare these three on identity alone
The three compounds are frequently grouped as GLP-1-family analogues, but they are chemically distinct molecules with separate CAS registry numbers, different sequence lengths and different molecular weights. For any laboratory handling reference material, identity is the first-order fact: the correct CAS number, formula and mass define what the vial is supposed to contain, and independent mass-spectrometry testing is what confirms it. The sections below give the documented identity of each, followed by a side-by-side summary and a note on how identity is verified analytically.
Semaglutide chemical identity
Semaglutide is a 31-residue peptide based on the human GLP-1(7-37) backbone, carrying substitutions at positions 8 and 34 and a C18 fatty-diacid moiety attached through a linker at position 26. It is classified in the literature as a mono-agonist at the GLP-1 (glucagon-like peptide-1) receptor.
- CAS registry number: 910463-68-2
- Molecular formula: C187H291N45O59
- Molecular weight: approximately 4113.58 g/mol
- Chain length: 31 amino acids
- Documented target class: GLP-1 receptor agonist
Tirzepatide chemical identity
Tirzepatide is a 39-residue peptide built on a GIP-related backbone, stabilised by an α-aminoisobutyric acid (Aib) residue at position 2 and conjugated to a C20 fatty-diacid moiety. It is documented as a dual agonist at the GIP (gastric inhibitory polypeptide) and GLP-1 receptors. Its molecular mass is the largest of the three compounds discussed here.
- CAS registry number: 2023788-19-2 (PubChem CID 156588324)
- Molecular formula: C225H348N48O68
- Molecular weight: approximately 4813.45 g/mol
- Chain length: 39 amino acids
- Documented target class: dual GIP and GLP-1 receptor agonist
Retatrutide chemical identity
Retatrutide is also a 39-residue peptide, with Aib residues at positions 2 and 20 and a C20 fatty-diacid moiety at position 17. In the literature it is classified as a triple agonist spanning the GIP, GLP-1 and glucagon receptors, which distinguishes its documented target profile from the other two. Its formula and mass sit between semaglutide and tirzepatide.
- CAS registry number: 2381089-83-2
- Molecular formula: C221H342N46O68
- Molecular weight: approximately 4731.33 g/mol
- Chain length: 39 amino acids
- Documented target class: triple GIP, GLP-1 and glucagon receptor agonist
Side-by-side identity summary
Read purely as chemistry, the three separate cleanly. Semaglutide is the shortest chain (31 residues) and the lowest mass; tirzepatide and retatrutide are both 39-residue chains, with tirzepatide the heavier of the pair. Each holds its own CAS registry entry, so they are never interchangeable as reference standards.
- Semaglutide (GLP1-SM): CAS 910463-68-2, C187H291N45O59, ~4113.58 g/mol, 31 residues, GLP-1 mono-agonist class
- Tirzepatide (GLP2-TZ): CAS 2023788-19-2, C225H348N48O68, ~4813.45 g/mol, 39 residues, GIP/GLP-1 dual-agonist class
- Retatrutide (GLP3-RT): CAS 2381089-83-2, C221H342N46O68, ~4731.33 g/mol, 39 residues, GIP/GLP-1/glucagon triple-agonist class
Confirming identity and purity by mass spectrometry
A registry number and a printed formula describe what a peptide should be; analytical testing establishes what a given batch actually is. Peptide identity is confirmed by matching the measured monoisotopic or average mass against the theoretical molecular weight using high-resolution mass spectrometry (LC-MS and HRMS), while chromatographic purity is assessed by the area of the main peak relative to related-substance and truncation peaks. Because tirzepatide and retatrutide are both 39-residue chains with similar masses, mass accuracy and orthogonal fragmentation matter when distinguishing them.
At livvmore, each research batch is identity- and purity-tested at the USC Alfred E. Mann Multi-Omics Mass Spectrometry Core, a university laboratory, by LC-MS and HRMS, and the resulting Certificate of Analysis is published per batch. When reading a COA, the fields that establish identity are the reported measured mass against the expected molecular weight, the batch number, the analytical method, and the percentage purity. Details of the methodology are described on the quality and testing page, and the wider incretin-family research range is grouped in the GLP research collection.
For laboratory research use only. Not for human or veterinary use.
Frequently asked questions
What are the CAS numbers of tirzepatide, semaglutide and retatrutide?
Tirzepatide (GLP2-TZ) has CAS 2023788-19-2, semaglutide (GLP1-SM) has CAS 910463-68-2, and retatrutide (GLP3-RT) has CAS 2381089-83-2. Each compound holds a distinct CAS registry entry, so they are separate reference materials and are not interchangeable.
How do the molecular weights of the three peptides compare?
By approximate average molecular weight, semaglutide is the lightest at about 4113.58 g/mol (C187H291N45O59), retatrutide is about 4731.33 g/mol (C221H342N46O68), and tirzepatide is the heaviest at about 4813.45 g/mol (C225H348N48O68). Figures are as recorded in PubChem and primary chemical registries.
How many amino acids does each compound contain?
Semaglutide is a 31-amino-acid peptide based on the human GLP-1(7-37) backbone. Tirzepatide and retatrutide are each 39-amino-acid peptides built on a GIP-related backbone stabilised by α-aminoisobutyric acid (Aib) residues.
What receptor-target class is each compound assigned in the literature?
In the published literature, semaglutide is documented as a GLP-1 receptor mono-agonist, tirzepatide as a dual GIP and GLP-1 receptor agonist, and retatrutide as a triple GIP, GLP-1 and glucagon receptor agonist. These are structural and pharmacological classifications of the molecules only.
How is the identity of these peptides confirmed in a laboratory?
Identity is confirmed by matching the measured mass against the theoretical molecular weight using high-resolution mass spectrometry (LC-MS and HRMS), with chromatographic purity assessed from the main-peak area. At livvmore each batch is tested at the USC Alfred E. Mann Multi-Omics Mass Spectrometry Core and reported on a per-batch Certificate of Analysis.